Fall 2013
EELE 250 Circuits, Devices, and Motors
Lab #2: Parallel and Series Resistors
Scope:
•
•
•
•
•
Use a multimeter to measure resistance, DC voltage, and current
Use the color code for resistors.
Use the prototype-board (breadboard)
Understand the terms “open circuit” and “short circuit”
Practice presenting laboratory results in a professional manner
Home preparation:
•
•
•
•
Review Chapters 1 and 2 of the Hambley text.
Read through the experiment and plan out each step.
Calculate the theoretical values for all electrical parameters you will be
measuring in the lab, and fill out the prelab sheets (see the last two pages).
Create tables in your notebook that you will use to record the calculated and
measured results for the experiment.
The nominal resistance value and its tolerance for 5, 10, and 20% resistors are
indicated by four colored bands (ABCD) on the resistor body.
A B C
D
C
Value given by digits: AB x 10 , and D indicates tolerance. Note that tighter
tolerance (1%) resistors have 5 bands (3 significant digits rather than 2).
The numerical values corresponding to the colors are:
0=
1=
2=
3=
4=
Black
Brown
Red
Orange
Yellow
5=
6=
7=
8=
9=
-1=
Green
Blue
Violet
Gray
White
Gold
Tolerance:
20% =
10% =
5% =
No band
Silver
Gold
Example: Brown Black Red Gold = 10 x 102 = 1000 = 1 kΩ ±5%
1
EELE 250 Lab #2
Fall 2013
Laboratory experiment:
1. Parallel Resistors
Breadboard the circuit shown in Figure 2.1, using the DMM to set the power supply
voltage. Use the DMM to measure the resistance of each resistor and record the
values in your lab notebook. Measure the indicated currents and record in your lab
notebook using the form shown in Table 2.1. Compare your measurements to the
values you calculated in the prelab.
I5
I3
Figure 2.1
I1
I2
I4
RECALL that to measure current you need to figure out how to insert the meter in series with
the branch and in the proper polarity in order to measure each current.
a. Calculate the ratio Rin= V1/I5 (Note: This ratio of applied voltage and
the input current is called input resistance, which is the equivalent
resistance “seen” by the voltage source).
Rin =
.
b. How does I5 compare with the sum of I3 + I4? What circuit law refers
to this summation? Do your measurements match your
expectations? Explain.
c. Can you find other similar relations among the measured currents
in this circuit?
2. Disconnect one of the terminals of the resistor R4 in the circuit shown in Fig. 2.1
(creating an open circuit in that branch), and repeat the measurements you did in
Part 1. Present the results of your prelab calculations and the measurements in
your notebook using the form shown in Table 2.1.
2
EELE 250 Lab #2
Fall 2013
Table 2.1: Parallel Circuit Calculations and Measurements
Part 1 (Fig. 2.1 with R4 connected)
Currents
Prelab Calculated
Values
Measured Values
Part 2 (Fig. 2.1 with R4 disconnected)
Prelab Calculated
Values
Measured Values
I1
I2
I1 + I2
I3
I4
I3 + I4
I5
Comment on the currents when R4 is connected and disconnected.
I
VA
VB
+
VR1
VC
+
VR2
—
Figure 2.2
—
VD
+
VR3
—
3. Series Resistors
Use the DMM to measure the resistance of each resistor and record the values in
your lab notebook. Breadboard the circuit shown in Figure 2.2 and (a) measure the
node voltages VA, VB, VC, VD with respect to the source voltage ground, (b) measure
the individual voltage drops across the resistors (VR1, VR2, VR3), and (c) measure the
current I through the circuit elements. Record the measurements in your lab
notebook using the form shown in Table 2.2.
a. How does the sum of VR1 + VR2 + VR3 compare with the applied
voltage V1? What circuit law is verified?
b. Calculate the ratio between applied voltage V1 and input current I:
Rin = V1/I =
.
3
EELE 250 Lab #2
Fall 2013
4. Connect a jumper wire on your breadboard between the terminals of R1. You
have established what is called a SHORT CIRCUIT across R1. Now repeat the
calculations and measurements of Part 3 for the circuit with R1 “shorted.”
Present the calculations and measured results of experiment Part 3 and Part 4 in
your notebook using the form shown in Table 2.2.
Table 2.2: Series Circuit Calculations and Measurements
Part 3 (Fig. 2.2 with R1 connected)
Measure
Prelab Calculated
Values
Measured Values
Part 4 (Fig. 2.2 with R1 shorted)
Prelab Calculated
Values
Measured Values
I
VA
VB
VC
VD
VR1
VR2
VR3
VR1+ VR2+ VR3
Before leaving lab, show your notebook with recorded lab results to your instructor for credit. Turn off all
equipment and return cables to their proper place. Leave your lab station clean and ready for other
students to use. You do not leave until your TA checks and approves the condition of your lab
station!
4
EELE 250 Lab #2
NAME:
PRELAB SHEETS
Perform the calculations before coming to lab, and show a summary of your work. Your
lab TA will collect these sheets at the start of the lab period for grading.
A. Using a resistor band color code chart, determine the color codes of the resistors to be
used in this lab and record the colors in the table below and in your lab notebook.
Resistor Nominal
Value (Ω)
Color Band 1
Color Band 2
Color Band 3
Color Band 4
Color Band 5?
1 kΩ
3.3 kΩ
10 kΩ
B. Calculate the indicated currents for the circuit in Figure 2.1 and place the results in the
table below and in your lab notebook.
Part 1 (Fig. 2.1 with
R4 connected)
I1
I2
I1 + I2
I3
I4
I3 + I4
I5
C. For the circuit in Figure 2.1 but with one of the terminals of the resistor R4 disconnected,
re-calculate the currents when the R4 branch is an open circuit.
Part 2 (Fig. 2.1 with
R4 DISCONNECTED
I1
I2
I1 + I2
I3
I4
I3 + I4
I5
Prelab page 1
EELE 250 Lab #2
NAME:
D. Calculate the indicated current and voltages for the circuit in Figure 2.2 and place
the results in the table below and in your lab notebook.
Part 3 (Fig. 2.2 with R1
connected)
I
VA
VB
VC
VD
VR1
VR2
VR3
VR1+ VR2+ VR3
E. Calculate the indicated current and voltages for the circuit in Figure 2.2 but with
resistor R1 replaced by a short circuit, and place the results in the table below
and in your lab notebook.
Part 4 (Fig. 2.2 with R1
shorted)
I
VA
VB
VC
VD
VR1
VR2
VR3
VR1+ VR2+ VR3
Prelab page 2